Phoebe's past writ large in craters

Saturn's moon shows its age

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Photographs from Cassini's flyby of Saturn's moon Phoebe have revealed a battered body, with an interesting past. Its face is pock-marked with craters ranging from 80 kilometers across to less than one kilometer, with variations in colour suggesting it contains plenty of ice.

The larger impact sites have prompted speculation that collisions in Phoebe's past could have blasted off enough material to have formed Saturn's smaller retrograde moons.

The brighter craters are most likely the newer impacts. Each collision would have blasted off surface material, and exposed brighter material, possibly ice, below the surface. There is more evidence for this theory on the crater walls: darker material seems to have slid down slope, exposing more light-colored material.

"What we are seeing is very neat. Phoebe is a heavily cratered body. We might be seeing one of the chunks from the formation of the solar system, 4.5 billion years ago. It's too soon to say," said Dr. Torrence Johnson, from NASA's Jet Propulsion Laboratory. "It's important to see the big picture from all of the other instruments to get the global view on this tiny moon."

All 11 of Cassini's instruments were pointed at the moon as the spacecraft flew by, just over 2000km above the surface. The data will be analysed over the next few days and will help scientists to build global maps of the moon, and to determine its composition, mass and density. ®